1. Field of the Invention
The present invention relates to a yaw control-by-rudder type tidal stream power generation apparatus and a method for controlling the same, and more particularly, to a yaw control-by-rudder type tidal stream power generation apparatus and a method for controlling the same in which a nacelle is adapted to be rotated according to the changed flow direction of a tidal stream using drag and lift applied to the rudder.
2. Description of the Prior Art
Tidal stream power generation refers to a power generation method that generates power using the flow of seawater. Unlike tidal power generation which generates power using a sea level change by installing a breakwater on a shore, the tidal stream power generation rotates a turbine installed under the sea using sea currents without installing a dam or a breakwater in a sea area where rapid seawater streams appear.
Since the tidal stream power generation does not require construction of a breakwater and thus costs less than the tidal power generation. The tidal stream power generation is evaluated as being environmentally friendly in view of the fact that ships may freely sail, fish migrations are not disturbed, and the surrounding ecosystem is not affected.
The tidal stream power generation may be generally classified into two types according to the direction of a stream and the direction of a rotating shaft of a rotor. That is, the tidal stream power generation is classified into a Horizontal Axis Turbine (HAT) type, in which the direction of the stream and the direction of the rotating shaft of the rotor are parallel to each other, and a Vertical Axis Turbine (VAT) type, in which the direction of the stream and the direction of the rotating shaft of the rotor are perpendicular to each other.
In connection of the HAT type, Korean Laid-Open Patent Publication No. 2012-0020293 discloses a turret type tidal stream power generation apparatus, which is technically characterized in that the power generation apparatus includes: a rotating shaft positioned under the water to correspond tidal stream; a rudder mounted on the rotating shaft to be rotated about the rotating shaft; and power generation units which are connected to the opposite sides of the rudder, respectively, a water wheel being positioned at one side of each of the power generation units.
In the Korean Laid-Open Patent Publication No. 2012-0020293, the power generation units are configured in a turret type to change the direction thereof according to a tidal stream to make the direction of the tidal stream and the oriented direction of the water wheel coincident to each other so that the power generation efficiency can be improved. In addition, as the direction of the tidal stream and the direction of the power generation units are made to be coincident to each other, resistance to a tidal stream force can be minimized so that the robustness can be enhanced.
However, conventional HAT type tidal stream power generation apparatuses including that of Korean Laid-Open Patent Publication No. 2012-0020293 have problems in that since the rudder is fixed to the direction of the rotating shaft of the water wheel, when the direction of the tidal stream is finely changed, the change of direction of the water wheel is delayed with a time interval rather than being instantly performed in a changed direction of the tidal stream, and when the direction of the tidal stream is reversed, it is difficult to make the direction of the power generation units coincident thereto.
In connection with this, Korean Patent No. 10-1056695 discloses a tidal stream power generation apparatus that corrects eccentricity, and a method of correcting the eccentricity. The tidal stream power generation apparatus of the Korean Patent No. 10-1056695 is characterized in that it includes: a blade positioned in front of the body of the tidal stream power generation apparatus and rotated by a tidal stream; at least one tail wing positioned on a rear side of the body of the tidal stream power generation apparatus and configured to be extendible in a horizontal direction of the body; an RPM gauge positioned inside of the body of the tidal stream power generation apparatus to measure a rotating speed of the blade; and a correction module positioned inside of the body of the tidal stream power generation apparatus to adjust the length of the tail wing based on the rotating speed of the blade which is measured by the RPM gauge.
In the Korean Patent No. 10-1056695, since the length of the tail wing is adjusted by the correction module included in the body so that the blade maintains its direction vertically in relation to the flow direction of the tidal stream, the efficiency of the tidal stream power generation can be maximized.
The conventional tidal stream power generation apparatuses including those disclosed in Korean Patent No. 10-1056695 may improve the power generation efficiency obtained by the blade by actively rotating the tidal stream power generation apparatus toward the flow direction of the tidal stream by adjusting the length of the tail wing whenever the flow direction of the tidal stream is changed. However, since the length of the tail wing (where lift and drag is generated by the flowing energy of the tidal stream) should be adjusted to rotate the tidal stream power generation apparatus whenever the flow direction of the tidal stream is changed, the power generation efficiency of the tidal stream power generation apparatus is rapidly reduced by the energy used for adjusting the length of the tail wing.
In addition, the conventional tidal stream power generation apparatus, which measures the rotating speed of the blade using the RPM gauge and the length of the tail wing is adjusted depending on the variation of RPM as disclosed in Korean Patent No. 10-1056695, has a disadvantage in that even if the running velocity of the tidal stream is changed, but the direction of the tidal stream is not changed, the length of the tail length is changed due to the change of RPM to rotate the blade which degrades the power generation efficiency.